The present invention relates to a fuel injector for gas turbine combustors and particularly relates to a multi-venturi fuel injector for catalytic and dry low-NOx applications.
The main components of a combustor for a gas turbine, for example, a catalytic combustor, include (1) a pre-burner which may typically constitute a diffusion style combustor that burns a small fraction of the fuel to elevate air temperature sufficiently to activate the catalyst downstream; (2) a pre-mixer which includes the main fuel injector and accomplishes fuel and air mixing; (3) a catalyst which partially converts the fuel in a flameless reaction in which no NOx is produced; and (4) a burn-out zone which includes homogeneous combustion in a post-catalyst liner of the lean fuel/air mixture flowing from the catalyst which does not generate NOx due to the relatively reduced temperature of the combustion. This type of combustor is capable of generating very low emissions.
A multi-venturi tube has been used in a catalytic combustor as a main fuel injector. See, for example, U.S. Pat. Nos. 4,845,952 and 4,966,001. These arrangements are intended to provide a uniform fuel/air mixture at the catalyst inlet. It will be appreciated that tight uniformity of the fuel distribution must be maintained over the large cross-sectional area at the catalyst inlet. Fuel/air mixing is accomplished by distributing the fuel among the large number of venturis that fill up the cross-section of the combustor followed by aerodynamic mixing inside the venturi tube as well as in the downstream region between the venturi exit plane and the catalyst inlet. In addition to uniform fuel/air mixture, the catalyst requires a uniform temperature and a uniform velocity across the catalyst inlet plane. Absent either one of these factors, the catalyst does not function optimally. It will also be appreciated that multiple venturi tubes produce laminar flow which suppresses large scale mixing and preconditions the flow such that only local mixing can be accomplished between the diffuser exit and the catalyst inlet. That is, mixing in that cross-sectional region is limited. For example, if a region of flow has a high temperature or velocity in comparison to the remaining flow, the thermal or velocity mal-distribution will deleteriously appear at the catalyst inlet. Accordingly, there is a need for a fuel injector for a gas turbine combustor affording improved uniform fuel/air, temperature and velocity distributions to the catalyst inlet.